An industrially extensively employed technique for imparting functions such as release properties, water repellency, and oil repellency to substrates such as polymer films, polymer sheets, polymer moldings, and coating films is to treat surfaces of these substrates to reduce the surface energy thereof.
For example, in pressure-sensitive adhesive tapes and pressure-sensitive adhesive sheets, a release agent containing low-energy functional groups such as long-chain alkyl groups, perfluoro groups, or polydimethylsiloxane groups is applied to the tape or sheet substrate on its back surface which comes into contact with a pressure-sensitive adhesive or to a separator to thereby reduce the surface energy thereof for the purpose of protecting the pressure-sensitive adhesive surface until use and facilitating the unwinding or release of the pressure-sensitive adhesive tape or sheet at the time of use.
Also in the case of films, sheets, moldings, coating films, and the like which are required to have water repellency and oil repellency, the surface energy thereof is reduced by applying a water and oil repellent containing low-energy functional groups such as long-chain alkyl groups, perfluoro groups, or polydimethylsiloxane groups to the substrate surface or incorporating the water and oil repellent into the substrate.
In order to obtain a durable low-energy surface by these treatment methods for surface energy reduction, it is necessary to use a polymeric material, i.e., polymer, having low-energy functional groups as the release agent or as the water and oil repellent. Where an especially high degree of durability is desired, a technique is generally employed to form a layer of a polymer containing low-energy functional groups on a surface of a base and then cure the polymer layer through a crosslinking reaction.
However, in the conventional technique using a polymer containing low-energy functional groups, the polymer is diluted with a solvent to prepare a treating liquid and this treating liquid is applied to a substrate surface and heated to volatilize the solvent to thereby form a thin polymer layer. This technique has the following disadvantages. When the polymer used is a polymer poorly soluble in general solvents, e.g., a polymer containing perfluoro groups, it is necessary to use an expensive fluorochemical solvent. When the polymer used contains long-chain alkyl groups, use of a heated solvent and much time for dissolution are necessary.
Where a thin polymer layer is formed and then crosslinked through a crosslinking reaction by heating the same at high temperature or irradiating the same with a radiation such as electron beams or ultraviolet, this technique not only is disadvantageous in procedure and cost, but has a drawback that the film, sheet, or other substrate is apt to suffer mechanical damage, e.g., thermal deformation.